Natural sesquiterpenes inhibit the genotoxicity induced by cigarette butts in the bacterial reverse mutation assay.

Tobacco smoke is one of the greatest threats to human health and the leading cause of preventable death in the industrialized society. Among tobacco-containing products, cigarette represents the most commonly used. After cigarette combustion, a waste portion, defined as cigarette butt, is discarded. It consists of a filter, which retains in the matrix toxic smoke components, among which carcinogens and irritant substances. In spite of their benefits to smokers, cigarette filter pose a serious litter and toxic waste disposal problem, due to their not biodegradability and the persistence of many toxic chemicals. Therefore, cigarette butts need to be manipulated as special waste, with potential risks to human and environmental health. In present study, the genotoxicity risk of the cigarette butts was evaluated in the bacterial reverse mutation assay. Then, the ability of the natural sesquiterpenes β-caryophyllene (CRY) and β-caryophyllene oxide (CRYO) to inhibit their mutagenicity was studied, as a possible prevention strategy. A methanolic extract from the smoked Marlboro Silver cigarette residues (CBE, cigarette butt extract) was used as butt sample. The mutagenic effect of CBE was evaluated on Salmonella tiphymurium TA98 and TA100 and Escherichia coli WP2uvrA strains, both in the absence and presence of an exogenous CYP450-enriched metabolic activator (S9) (Di Sotto et al., 2014). Thereafter, the antimutagenicity of CRY and CRYO was studied against CBE. In order to study the potential mechanism involved in the antimutagenicity of the extracts, three different protocols (pre-, co- and post-treatment) were applied. Results obtained showed that CBE produced mutagenic effects (increasing about twice the number of revertant colonies) in all the strains tested but only in the presence of the exogenous metabolic activator S9. The concentration of 0.3 mg/ml produced a sub-maximal mutagenic effect in all strains and was used in the antimutagenicity assay. Both sesquiterpenes (CRY 0.43-1.7 mg/m and CRYO 0.09-0.34 mg/ml) significantly reduced the CBE-induced revertant colonies, although with different potency and specificity. Antimutagenicity of CRY and CRYO was similar in S. tiphymurium strains, in all treatments. In contrast, CRYO was the most active compound in E. coli WP2uvrA, being the antimutagenic effect strong at all concentrations and protocols, while the CBE-mutagenicity inhibition produced by CRY was mostly moderate. In cell survival experiments, test compounds never produced cytotoxic effects in the presence of CBE. Present results allow hypothesize the involvement of multiple mechanisms (both desmutagenic and bioantimutagenic) in the antimutagenicity of the sesquiterpenes tested. Taking into account the potential toxicity due to cigarette butt exposure, also considering the mutagenic power here highlighted, CRY and CRYO appear to be possible further candidates as environmental decontaminants against this hazardous waste.